Chronic kidney disease (CKD) is a health condition characterized by progressive decline in kidney function. As kidney function worsens, patients with CKD experience increasing levels of physical and emotional distress, a variety of co-morbidities, and ultimately the need for dialysis and kidney transplantation. Although children constitute a small proportion of the total CKD population, the expected lifespan of a child <14 years-old on dialysis is just 20 years. It has been challenging to conduct clinical trials and epidemiological studies for pediatric CKD because it is a rare disease. In 2003, the NIDDK initiated the CKiD study, an ongoing Chronic Kidney Disease in Children Cohort Study, which is examining risk factors for progression of pediatric CKD and the evolution of related co-morbidities. The CKiD study has enrolled 891 children from over 50 pediatric nephrology centers (25% of the nation's pediatric nephrologists participate) and collected longitudinal phenotypic information, producing substantial new knowledge on kidney disease and its sequelae. CKiD is a unique, national network for evaluating PROMIS Pediatric measures. The purpose of the proposed project is to evaluate the content validity, clinical meaning, responsiveness, and longitudinal construct validity of four PROMIS pediatric instruments (pain interference, fatigue, psychological stress experiences, and positive affect) in 200 children at increased risk of accelerated kidney function decline. As a panel, these measures characterize a child's level of suffering and happiness. Relieving suffering by reducing disease activity or palliating symptoms in order to promote a child's well-being and happiness is often the primary objective of medical treatment for pediatric chronic conditions. The project will be one of three linked studies within the Child-Centered Outcomes in Practice and Research (COPR) Center's program of research. Each will use similar measures, methods, and methodological infrastructure to examine the clinical validity of PROMIS among children who are chronically ill. Our specific aims are to: (Aim1) Assess the content validity of the PROMIS Pediatric pain interference, fatigue, psychological stress experiences, and positive affect measures for children with CKD; (Aim 2) Establish clinically meaningful classifications for the PROMIS Pediatric pain interference, fatigue, psychological stress experiences, and positive affect measures for children with CKD; (Aim 3) Estimate minimal important differences (MIDs) for the PROMIS Pediatric pain interference, fatigue, psychological stress experiences, and positive affect measures in children with CKD; and, (Aim 4) Evaluate the longitudinal construct validity of PROMIS Pediatric pain interference, fatigue, psychological stress experiences, and positive affect measures among children with CKD. If our aims are achieved through the clinical validation of the PROMIS instruments in the well phenotyped children in the CKiD study, we will take major steps toward facilitating the use of PROMIS as standard outcomes in routine clinical practice and standard end-points in clinical trials for children with chronic kidney disease.